1. Field of the Invention
This invention relates to an object information acquiring apparatus and an object information acquiring method.
2. Description of the Related Art
The research of optical imaging technology capable of obtaining information in a living subject by irradiating light to the living subject from a light source such as a laser is being actively pursued in the medical field. Photoacoustic Tomography (PAT) is one of the optical imaging technologies. A photoacoustic tomography device irradiates pulsed light generated from the light source to the living subject, and uses a probe to receive, in various positions, an acoustic wave (typically an ultrasound wave) that is generated when the body tissue, which absorbed the light energy that propagated and diffused in the living subject, instantaneously expands. It is thereby possible to detect, for instance, the difference in the absorption factor of light energy in the suspected site of a tumor or the like and other tissues.
Subsequently, the image reconfiguration region (region where information in the living subject is to be imaged) is divided into a plurality of voxels or pixels. In addition, image reconfiguration is performed by using the received signal of the timeframe in which the acoustic wave reaches the elements of the probe from the voxels or pixels. For the image reconfiguration process, FBP (Filtered Backprojection), DELAY-AND-SUM and other well-known methods may be used. It is thereby possible to obtain the optical characteristic value distribution such as the initial sound pressure distribution or the absorption coefficient distribution in the living subject. As a result of performing photoacoustic measurement using light of various wavelengths, it is possible to quantitatively observe a specific substance in the object; for example, measure the hemoglobin concentration contained in the blood or measure the oxygen saturation of the blood.
In Photoacoustic Tomography, a probe is used to receive the acoustic wave. In the field of ultrasound diagnostic devices that similarly receive acoustic waves using a probe, it is known that the receiving sensitivity of the probe depends on the incidence angle of the acoustic wave that enters the probe (NPL 1: “Ultrasound Wave Diagnostic Device” Co-authored by Masayasu Ito and Tsuyoshi Mochizuki, Published by Corona Publishing Co., Ltd., Aug. 26, 2002). In other words, as the incidence angle of the acoustic wave that enters the probe increases, the receiving sensitivity of the probe decreases, and there is a problem in that imaging of favorable directionality cannot be performed.
Thus, Japanese Patent Application Publication No. S60-021744 (PTL 1) discloses a method of correcting the differences in the receiving sensitivity caused by the incidence angle. In PTL 1, the probe transmits the acoustic wave at a certain angle, and receives the reflected wave from the object. In addition, the sensitivity difference which arises according to the incidence angle of the acoustic wave is corrected by changing the amplification factor for each element of the probe, and the sensitivity of the respective elements is caused to be uniform so as to enable imaging of favorable directionality.
Patent Literature 1 (PTL 1): Japanese Patent Application Publication No. S60-021744
Non Patent Literature 1 (NPL 1): “Ultrasound Wave Diagnostic Device” Co-authored by Masayasu Ito and Tsuyoshi Mochizuki, Published by Corona Publishing Co., Ltd., Aug. 26, 2002